The projection of single Ia fibers to gamma-motoneurons is studied in this laboratory. We will examine the projection to axotomized motoneurons. We will also study the projection of single Ia fibers to gamma-motoneurons in spinal cord segments just caudal to hemisection. We have made extensive studies of projections of single triceps surae Ia afferent fibers to homonymous and heteronymous motoneurons in normal animals. Our interest lies in observing the changes in these projections under the experimental conditions described above. We are also interested in the reflex specificity exhibited by grafted supernumerary limbs of Xenopus laevis innervated by thoracic spinal nerves. We will ascertain the extent to which thoracic sensory neurons have atypical central projections as a result of the presence of the grafted limb. These studies will make use both on physiological and anatomical techniques. Does stimulation of thoracic dorsal roots result in the short latency lumbar ventral root responses characteristic of stimulation of lumbar dorsal roots? Can thoracic sensory neurons be shown to project more strongly to lumbar segments in these experimental preparations than in normal ones? BIBLIOGRAPHIC REFERENCES: Mendell, L.M. and Scott, J.G. The effect of peripheral nerve cross union on connections of single Ia fibers to motoneurons. Exp. Brain Res., 22: 221-234, 1975. Hollyday, M. and Mendell, L.M. Area specific reflexes from normal and supernumerary limbs of Xenopus laevis. J. Comp. Neurol., 162: 205-220, 1975.